Abstract: Effects of sulfur dioxide (SO₂) pretreatment on physiological responses of Arabidopsis thaliana to drought stress were investigated. Test plants were comprised of control group, 30 mg·m^-3 SO₂ exposure group, drought stress group and 30 mg·m^-3 SO₂ exposure followed by drought stress group. The results showed that leaf relative water content (LRWC) decreased and leaf wilting increased with increasing drought stress and extension of time for drought stress. SO₂ pretreatment alleviated leaf wilting and maintained higher relative water content under drought conditions. LRWC in SO₂ pretreatment group increased by 4%-10% compared to drought stress group. Moreover, drought stress induced high levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), while SO₂ pretreatment decreased the contents of H₂O₂ and MDA by 10%-19% and 15%-18%, respectively, under drought conditions. Meanwhile, the contents of proline and soluble sugar were significantly increased by 15%-30% and 6%-31% in SO₂ pretreatment group, respectively. In addition, the results of RT-PCR analysis showed that DREB2A, DREB2B, CBF4 and RD29A genes were all upregulated in response to drought stress. These droughtresponsive genes showed higher transcript levels in SO2 pretreatment group than in drought stress group, among which the relative expression level of RD29A increased by 16%. Our results suggested that SO2 pretreatment could improve drought adaptation in Arabidopsis plants by upregulating droughtresponsive genes, alleviating the oxidative stress and promoting the accumulation of osmotic adjustment substances.

Key words: power law., grassland, loess hilly area, spatial pattern, slope aspect